1. Field of the Invention
This invention relates to an integrated circuit card, and more particularly to an improvement of integrated circuit card in which a plurality of volatile semiconductor memories are provided within a thin rectangular card together with a battery.
2. Description of the Related Art
Heretofore, this type of integrated circuit cards (hereinafter referred to as "IC cards") have been developed as cashing cards, personnel identification cards for identifying a particular individual, credit cards, and tag cards attached to particular goods for specifying a designation, etc.
This IC card constitutes one system with a card processing device (that is "a card reader"). The IC card is inserted into a part to be inserted of the card reader, and the external connecting terminal of the IC card is electrically connected to the contact in the card reader, so as to be able to read the information in the IC card.
FIG. 1 shows the internal construction of the IC card in general. The memory section of the IC card 1 has a plurality of random access memories (hereinafter referred to as "RAM") 2 that are volatile semiconductor memories.
In the IC card 1, a part of address input signal S1 is input to a decoder 3 to decode it, and a chip enable signal S3 corresponding to a specified one of the RAM 2 is set to a value "1", so as to select the specified RAM 2 from the memory section. When the IC card 1 becomes usable by being inserted into a card reader (not shown), the decoder 3 detects an enable signal S2 having the basic value "1" which is to be inputted to an input terminal E to be controlled to the active state.
In addition, when the IC card 1 becomes inactive by removing from the card reader, the decoder 3 detects that the enable signal S2 provided to the input terminal E has a logic value "0", so as to switch all the chip enable signal S3 to the value "0". All of the RAM 2 is controlled to enter a deselected state.
Power supply to be supplied to the plural RAM 2 is switch controlled by a power supply switching circuit 4. The power supply switching circuit 4 has two input terminals IN.sub.1 and IN.sub.2 for inputting supply voltage V.sub.CC2 of, for example, 5V supplied from the card reader, and voltage V.sub.CC1 of, for example, 2V supplied from an internal battery 5. The power supply to be supplied to the RAM 2 is switch controlled in accordance with the potential difference between these input terminals IN.sub.1 and IN.sub.2. If the power supply switching circuit 4 detects that the supply voltage V.sub.CC2 is inputted, it supplies the supply voltage V.sub.CC2 from output terminal OUT to the power supply terminal V.sub.CC of the RAM 2. If the power supply switching circuit 4 detects that the supply voltage V.sub.CC2 is not inputted, it supplies the voltage V.sub.CC1 of the internal battery 5 to the power supply terminal V.sub.CC of the RAM 2.
Therefore, when the IC card 1 is inactive because of its separation from a card reader, and the supply voltage V.sub.CC2 is not supplied, the RAM 2 retain data which has been stored by the voltage V.sub.CC1 supplied from the internal battery 5. As the internal battery 5, for example, a very thin battery, such as, a paper battery, is used to enable the IC card 1 to have a thickness of 1 or less. The paper battery has a small capacity as a power supply due to its very limited thickness, and is, in effect, used only to retain data in the RAM 2. The life of IC cards thus depend on the life of the internal battery.
However, in the memory section of a conventional IC card 1, all of the RAM 2 have the construction that a power supply is supplied from the internal battery 5, and constantly consume the same amount of current whether or not valid data has been written to the RAM. As a result, there is a problem that the amount of current consumed by the memory section, while the IC card 1 is inactive, increases with the number of RAM 2 mounted in the IC card 1, resulting in a reduced life of the internal battery 5.
More specifically, the conventional IC card 1 has the disadvantage that the data memory time by the RAM 2, that is, the life of the IC card 1, decreases with the increasing number of RAM 2. Another disadvantage of the conventional IC card 1 is that the internal battery 5 is not used efficiently because the RAM 2 consume the same amount of current whether or not valid data has been written to the RAM 2.
As a method for solving this problem, it is considered to recharge the internal battery 5 when its life has expired. However, this solution is inadequate because the recharge frequency and thus the needless bother increase with the number of RAM 2, and users generally have difficulty in replacing the batteries 5 in such IC cards 1.
To eliminate this disadvantage, an internal battery 5 with a large capacity can be employed. In this case, however, it is difficult to provide a thin card because the battery must be large to have a large capacity, and the thickness of the IC card is dependent upon the size of the internal battery.